Piedl et al., PCT Pub. No. WO 00/25416, published May 4, 2000, discloses a system for controlling a pump load, in which the pump is coupled to an electric motor through a crankshaft, such that pump operation is sensed indirectly to eliminate the need for a pressure sensor or a position sensor.
Bert et al., U.S. Pat. No. 6,074,170, shows that it is known in the art to sense pump pressure and to adjust the speed of the motor in response to pump pressure using a microcomputer. This system regulates pump pressure through a pressure loop operating at about 3 Hz.
A technical problem in driving a pump load with an electric motor is that the highly cyclic torque load of the pump produces a high RMS current in the motor, resulting in excessive heating in the motor and higher than necessary loading on the power source. If the electronic control for the motor is required to maintain a constant speed during this pump cycle, as is often specified, the RMS current problem becomes even greater. In order to solve this problem, many applications require that an inertial load in the form of a mechanical flywheel be added to the motor to even out or “level the load” placed on the motor.